The structural and organizational complexity of bacterial cells has become increasingly apparent over the last several decades. It is now well established that cell polarity, functional membrane microdomains, and discrete cytoplasmic protein- and membrane-bound compartments are prevalent in diverse bacterial species. Furthermore, disruption of these architectures can impair bacterial physiology and virulence-related behaviors. In many instances, however, there is an incomplete understanding of mechanisms underlying bacterial organization and how such organization affects cell physiology. This proposal describes the use of the purple nonsulfur bacterium (PNSB) Rhodopseudomonas palustris, as a model organism to evaluate how bacterial organelle development and localization affect (and are affected by) cell physiology. PNSB develop a membranous photosynthetic organelle (intracytoplasmic membrane, ICM) when grown under phototrophic conditions. Preliminary data demonstrate that natural autofluorescence of the photosystem pigment bacteriochlorophyll can be utilized in live cells to easily monitor the distribution patterns of ICM-associated photosystems. These systems are discretely localized in R. palustris in contrast to many other model PNSB in which ICM is present throughout the cell. We propose to take advantage of the differences in ICM structure and localization between PNBS species to evaluate correlations that may exist between ICM structure, photosystem organization, ICM inheritance, and modes of cell growth. We will also evaluate the importance of ICM dynamics for metabolic robustness in R. palustris. The specific aims of this proposal are to: (i) determine the temporal and spatial localization of R. palustris photosystems and their contribution to metabolic homeostasis, and (ii) identify genetic factors regulating R. palustris photosystem localization and characterize the physiological role of photosystem localization. A multidisciplinary approach will be taken to address these aims and will include cell biology (fluorescence light microscopy, electron microscopy), genetics (targeted and random mutagenesis), and chemistry (metabolic flux analysis using non-radioactive isotopes). Overall, these experiments will promote the understanding of how bacterial compartmentalization contributes to metabolic robustness and impacts cell physiology.